Diaphragm Wall Research Articles

Fiber-Optic Monitoring of a Twin Circular Shaft Excavation: Development of Circumferential Forces and Bending Moments in Diaphragm Walls

Fiber-Optic Monitoring of a Twin Circular Shaft Excavation: Development of Circumferential Forces and Bending Moments in Diaphragm Walls

Performance of a Deep Excavation Supported by Diaphragm Walls Combining with Servo Steel Struts: A Case Study in Hangzhou, China, Soft Clay Deposits

Performance of a Deep Excavation Supported by Diaphragm Walls Combining with Servo Steel Struts: A Case Study in Hangzhou, China, Soft Clay Deposits

Solution of inclinometer data processing for horizontal displacement: A case study of basement diaphragm wall monitoring in Vietnam

Abstract In the recent decade, Digitilt DataMate II and GK-604D inclinometer systems have commonly been used to evaluate horizontal displacement as well as to test the calculation models of basement diaphragm walls in Vietnam. The difference in the equipment constants as well as the calculation principle has confused the surveyors and even led to erroneous monitoring results. Furthermore, the use of commercial programs DigiPro2 and SiteMater, which are expensive, in inclinometer data processing requires a thorough understanding. Differences in calculation results between software occur due to the choice of the instrument constant, the rounding principle, or the choice of the reference point at the bottom of the monitoring pipe. In this paper, we summarize the calculation principles of Digitilt DataMate II and GK-604D inclinometer systems. To respond well to the data processing of inclinometer systems for basement diaphragm walls in Vietnam, we have developed the ICTool program that can efficiently calculate the observed data of the GK-604D system. The results of inclinometer data processing by the ICTool program are homogeneous in comparison with DigiPro2 and SiteMater software. In addition, the ICTool program was established to provide, free of charge, the communication of the monitoring of basement diaphragm wall displacement in Vietnam.

3D Simulation and Leakage Detection Technique for Deep Foundation Pits Based on Electric Field

To solve the problems of poor accuracy, poor anti-interference ability and unclear distribution of leakage electric field response characteristics of the traditional ground DC method for leakage detection of underground diaphragm walls in foundation pits, this paper proposes a deep foundation pit leakage detection technology based on the electric field. Secondly, it constructed the multi-field coupling equations and boundary conditions of the leakage electric field coupled with the leakage flow field and ion diffusion field, and then realized the three-dimensional forward evolution of the leakage electric field of the pit using the nonstructural mesh dissection method and the finite-element-infinite-element discretization method. Finally, physical model experiments and numerical simulations are used to confirm the reliability and accuracy of the foundation pit leakage detection technology and system. The results shows that monitoring the continuous change of the electric field for a period of time, the electric field detection technology for foundation pit leakage can effectively identify the location of hidden leakage and overcome the site’s strong industrial interference, resulting in a new technical solution for foundation pit leakage detection.

Optimization of lap splice positions for near-zero rebar cutting waste in diaphragm walls using special-length-priority algorithms

ABSTRACT Construction processes often result in rebar waste when cutting stock length rebar to required length, incurring significant costs and contributing to CO2 emissions. While prior research has explored rebar waste reduction through cutting pattern optimization, the potential gain from adjusting lap splice positions has been neglected. This study focuses on enhancing waste reduction by optimizing lap splice positions, particularly focusing on utilizing special length rebar to achieve a cutting waste rate below 1%. Our approach employs a three-step heuristic algorithm: (1) optimizing lap splice positions for alignment with special length rebar; (2) generating cutting patterns based on special length rebar; (3) creating cutting patterns for remaining rebars using stock length rebar. Applying this algorithm to a diaphragm wall at an interchange station adhering to the British Standard shape codes yielded remarkable results. The cutting waste decreased by 3,000.22 tons, the CO2 emissions reduced by 10,398.77 tons, and the cost savings totaled USD 3,480,108. Consequently, the cutting waste rate reached an impressive 0.77%. By adopting the principles outlined in this paper, construction practices can significantly reduce waste, promote sustainability, and mitigate financial losses associated with rebar waste.

Numerical study on the group wall effect of nodular diaphragm wall foundation in high-rise buildings

Abstract As a new type of foundation, the nodular diaphragm wall (N-D wall) has large transverse stiffness and high bearing capacity, with low noise and low vibration, which is suitable for high-rise buildings in cities with limited land area. The reduction coefficient of each load composition under the same displacement conditions and the ABAQUS finite element numerical analysis software are introduced to analyze the group effect of N-D wall foundations. The results show that the compressive group wall effect coefficient is greater than 1, while the uplift group wall effect coefficient is less than 1. Under the same displacement condition, the group effect of the compressive wall is more obvious than that of the uplift wall, and the group effect of the middle wall is more obvious than that of the sidewall. The wall group effect gradually develops downward with the increase in displacement. The ultimate compressive capacity is mainly controlled by the friction resistance, which is especially obvious in the sidewall. The cap resistance load-sharing ratio decreases first and then increases with the settlement. The cap resistance is not evenly distributed, the stress at the corner is the lowest, and the stress is mainly concentrated in the middle. The influence of wall spacing, length, and width on the uplift bearing capacity is highly significant, while the influence of nodular part angle is slightly significant. The influence of wall width, length, and spacing on compressive bearing capacity is highly significant, while the influence of nodular part angle is weak. The influence of nodular part angle on the uplift bearing capacity of group wall foundation is stronger than that of the compressive bearing capacity.

Introducing the zero-trim pile technique: a more sustainable alternative to pile cropping

Standard practice for bored concrete pile construction is to over-pour the concrete and crop the piles down after curing to ensure they are sound at cut-off level. This paper introduces an innovative ‘zero-trim pile’ technique, which has been trialled on the UK’s High Speed Two railway project. It eliminates the need for cropping by sucking out wet concrete above cut-off level. This increases safety, reduces noise, saves time, improves accuracy and avoids cracking. This paper reviews lessons learned from the trials and outlines steps for successful implementation of the technique on a wide range of in situ concrete piling and diaphragm walling projects.

Performance of an Asymmetric Pit-in-Pit Excavation Supported by Diaphragm Wall and Multi Uplift Piles System in Coastal Areas

The performance of asymmetric pit-in-pit excavation supported by diaphragm wall and multi uplift piles in coastal areas has been rarely reported. In this work, case study is conducted to investigate the mechanical characteristics of such excavation. A numerical model is established using the ABAQUS finite element platform, and its effectiveness is evaluated by comparing with the field monitoring data. After evaluation, the effects of uplift piles on excavation-induced deformations are investigated. Results show that the maximum wall deflections (δhm) are 0.02%~0.22% of the excavation depth (He), with the ground surface settlements of less than 0.6%·He and the settlement influence zone extending beyond 4He. As the soil is excavated, the top wall shows outward deformations to the active zone, and the transverse support is under tension. The use of combined diaphragm wall and multi uplift piles reduces the embedment ratio of diaphragm wall to a minimum value of 0.14, and decreases the δhm and rebound of base soil (δvrm) by 42% and 63%, respectively. A design suggestion is proposed for pile diameter (D), pile length (L) and pile spacing (S) to fall within the range of 0.4~0.8 m, 10~20 m and 6D~8D, respectively.

Supporting behavior evolution of ultra-deep circular diaphragm walls during excavation: Monitoring and assessment methods comparison

Ultra-deep circular excavations present unique challenges in geotechnical engineering due to their complex behavior and the scarcity of relevant case studies. This paper presents a comprehensive study on the excavation behavior of the deepest circular excavation (77.3 m) ever built in China through field monitoring and computational methods. The excavation process leads to the transformation of the underground diaphragm walls into an elliptical cylinder shape, elongated in one direction and shortened in the perpendicular direction. The outer annular reinforcement primarily experiences compressive stresses, while the inner annular reinforcements undergo tensile stresses, attributed to the spatial deformation of the cylinder structure. The findings emphasize the significance of considering 3D deformation and accurate characterization of internal forces to ensure the structural integrity and stability of such complex geotechnical systems. Three computational methods, including the 2D load-structure method, the 3D load-structure method, and the stratum structure method, were employed to analyze the deformation and internal forces. Comparison between measured data and calculated results reveals differences and highlights the effectiveness of the 3D load-structure and stratum structure methods in capturing the observed behavior. The study contributes to the understanding of circular excavation for designs in geotechnical engineering.

Stability Analysis of Trench Wall for Diaphragm Wall in Ultra-Deep Circular Foundation Pit: A Comprehensive Investigation

Circular diaphragm walls are increasingly being used in ultra-deep foundation pits due to their arch-shaped bearing system, which provides reasonable structural support. The trench walls that form the circular ground connection wall are typically double-angled in shape, and their stability analysis remains a challenge. In this paper, an instability model for double-angled trench walls based on 3D sliding body analysis is proposed. The objective of this paper is to determine the minimum amount of slurry needed to maintain the integrity of the trench wall. The results show that the center of symmetry on the inside of the wall is the most vulnerable to damage, followed by the inside corner, and then the center and corner on the outside. The consideration of sliding bodies in overall and local stability calculations for double-angled trench wall shapes can provide a reasonable stability assessment.

Effects of the ground surface thermal boundary condition on the long-term thermal performance of energy diaphragm walls

Energy diaphragm walls have attracted increasing attention due to their high heat transfer performance. Thus, the factors that affect the thermal performance of energy walls have been investigated to provide insights for further practical applications. Numerical simulation is widely used in energy wall analysis due to the complexity of conducting field tests. Therefore, the choice of boundary conditions in the simulations is crucial; it refers to whether the model reflects reality and has a significant impact on the results. In most cases, the assumed ground surface thermal boundary is not the same (e.g., thermal insulation, constant temperature), and the ground temperature is also assumed to be constant with depth, which may result in a large loss of thermal energy or inaccurate assessment of thermal performance for the energy wall. In this respect, this paper investigates the long-term differences in thermal performance under these boundaries and considers the ground temperature that varies with depth and time, which has not been comprehensively considered before in the analysis of energy walls. The results show that accounting for air temperature or ground temperature variations with depth and time can result in a great increase in thermal performance, e.g., a 34% increase in the cooling thermal load compared with the thermal insulation boundary. In the performed parametric analysis, the results highlight the significant influence of the thermal load and wall height on the thermal differences between these boundaries. These findings provide a reference for choosing ground surface thermal boundaries and better thermal design of energy diaphragm walls.

Suggested method of utilizing soil arching for optimizing the design of strutted excavations

An expression was derived for the soil arching effect behind foundation pits by considering the natural static equilibrium. An optimization strategy for super-large deep foundation pits was proposed based on the arching-related stress transformation and the limit span of soil arching. Steel–concrete composite piles that act as arching feet to formulate the soil arching are introduced. The proposed arching-effect methodology is supported using numerical modelling that reveals the stress arching in the principal stress contours. Once the interval between piles is less than the analyzed limit span of the soil arch, introducing steel–concrete composite piles can cause a sharp decline (by one third) in the wall deflection. It is essential that the steel struts are moved to the diaphragm wall where the steel–concrete composite piles form the arching feet and that the total number of steel supports remains unchanged. The formation of an arching foot can also significantly reduce the lateral wall deflection, enhancing the stability of the deep foundation pit during construction. Grouping the piles efficiently is a reliable tool for stabilizing deep foundation pits from the point of view of multi-arching action. Furthermore, the maximum principal stress contours reveal the arched trajectory between adjacent piles.

Three-Dimensional Numerical Analysis on the Influence of Buttress Wall Removal Timing on the Lateral Deformation of Diaphragm Walls during Deep Excavation

Urban areas in Taiwan are densely populated with limited land. Excavation often takes place near existing buildings, necessitating protective measures for adjacent properties. Among these measures, cross walls or buttress walls are commonly employed, especially in weak foundation soils, which have seen many successful applications. These mechanisms mainly contribute to reducing lateral deformation of the diaphragm walls, ground subsidence, and excavation face uplift. However, the behavior of these walls is essentially three-dimensional, and common engineering analyses employing one-dimensional elastoplastic beam analysis cannot adequately simulate their mechanical behavior. This study utilized the PLAXIS 3D 2018 software to analyze real-life cases of buttress walls and cross walls. Then, the results of the numerical models were validated against actual field measurements, and the outcomes were satisfactory, and within the regulatory allowable values. The primary objective of this study was to find the influence of different buttress wall removal timings on the lateral deformation of the diaphragm wall. The findings suggest that the gradual removal of buttress walls will effectively control the lateral deformation of diaphragm walls during the excavation of deeper floors like mezzanines.

Semi-Analytical Prediction of Ground Surface Heave Induced by Shield Tunneling Considering Three-Dimensional Space Effect

The ground surface deformation induced by shield tunnels passing through enclosure structures of existing tunnels is a particular underground construction scenario that has been encountered in Wuhan Metro Line 12 engineering cases in China. Timely ground deformation prediction is important to keep shield tunneling safe. However, the classic ground deformation theory is difficult to accurately predict for this ground deformation. This paper develops a semi-analytical method to predict ground heave considering the space effect in this engineering condition. Based on the improved ground deformation theory, a novel deformation prediction method for the ground and enclosure structure is derived and combined with Kirchhoff plate theory. Comparing with field deformation measurements, the maximum difference between the measured and calculated deformation is 14.6%, which demonstrates that the proposed method can be used to predict the ground heave induced by shield tunnels passing through the enclosure structure of existing tunnels. The parameters of the underground diaphragm wall used in Wuhan Metro Line 12 are further studied in detail. The results show that the ground heaves have a positive correlation with the embedded ratio of the diaphragm wall, but a negative correlation with its elastic modulus and thickness. However, the thickness and embedded ratio have a limited effect on ground heaves. This study provides a technical reference for optimizing the setting of enclosure structures in order to protect existing buildings.

Full-scale experiments and modeling of precast two-wall-in-one diaphragm wall components for oceanic artificial cities

An oceanic artificial city built by reclamation is an important solution for Hong Kong to solve the land supply conflicts. Traditional cast-in-situ enclosure structures face challenges for adapting to ocean geology, climate and environment. This study thus proposed a precast two-walls-in-one diaphragm wall (PTDW). This study first conducted a full-scale experiment for PTDW. Second, numerical studies of PTDW were performed. Third, a PTDW Bending-performance Assessment Model (PTDW-BAM) was developed. Finally, the parameter analysis and decision making were performed. The main conclusions are (1) PTDW using welded joints presented a resilient damage pattern. The joint damage was slighter and lagged behind the hollow section. (2) The PTDW components with welded joint constraint exhibited high adaptability to the oceanic artificial city project. The damage pattern exhibited joint closure and cracks without penetration. (3) Hollow section parameters are central for the bending performance of PTDW. PTDW-BAM comprehensively designed the hollow section parameters and obtained the optimal parameters. (4) PTDW-BAM has a designable and flexible parameter decision-making capability for oceanic artificial city projects. The results of PTDW-BAM in the case study presented resilience, weight reduction and tightness. This achievements provide green products and assessment tool for the oceanic artificial city construction in Hong Kong.

Shadowing pathology on diaphragm walls investigation

Nowadays, the densification of cities requires the multiplication of underground infrastructures like car parks and metro stations. It is in this context that has been established for 70 years now, the diaphragm wall technique. The construction works follow complex implementation operations that can generate some defects and cause the appearance of imperfections. Among these imperfections, shadowing pathologies is the main subject of this study. The objective is to better understand the different operations with the intention in explaining the formation of the pathology.An experimental study is presented to answer some questions related to the concrete. Thanks to a laboratory prototype called Beta Tank, two complementary campaigns were conducted. Using different exfiltration outcomes, and by varying the cementitious material, it was possible to recreate the shadowing pathologies. The results found from the experimental campaigns allowed identifying potential causes of the anomalies and helped in proposing some recommendations for the foundation materials and techniques.

Study on the Effect of Multi-span Pit Excavation on Supporting Structures Based on the Cutter Soil Mixing Method

The Cutter Soil Mixing (CSM) method, a relatively recent innovation, employs twin-wheel milling and profound agitating machinery for wall construction. In an endeavor to scrutinize the displacements and internal support stresses to the support structure during the excavation of a multi-span foundation pit founded upon the CSM method, a two-dimensional finite element model was established, utilizing the Midas GTS NX 2019 V1.2 finite element software. This model was grounded on a multi-span foundation pit excavation endeavor situated in the eastern expanse of China, where steel bracing and the CSM method assumed the preeminent mantle of support. A comprehensive scrutiny encompassed ten distinct working conditions, each juxtaposed and dissected to ascertain the displacements affecting the CSM wall and the forces exerted upon the support system during the foundation excavation process. The research findings manifest a certain interplay between the embedment depth of the CSM wall and the span of the pit excavation in shaping the displacement and support stresses within the supporting structure. While deeper embedment augments the potential for enhanced support outcomes, its efficacy remains constrained. As the embedment depth increases, the internal support moment and lateral displacement of the wall increase slightly. Taking a pit with a shallow embedded CSM wall as an example, wherein both the lateral and vertical displacements experience an ascent followed by a descent, culminating at the juncture of a four-span pit. Likewise, the axial force and bending moment exerted upon the steel supports undergo a similar trajectory, culminating with a two-span pit as the threshold. At the five-span, the maximum lateral displacement of the CSM wall exceeds that observed at the two-span by an increment of 21.14%. These findings offer invaluable insights into the embedment depth of diaphragm walls and the span of pit excavations, wielding profound implications for future undertakings akin to the foundation pits in question.

Bentonite and polymeric support fluids used for stabilization in excavations

Bentonite is a natural and finite mineral resource. Dilute suspensions of sodium montmorillonite clay in water represents bentonite slurries. Suspension and orientation of colloidal clay particles define rheological properties in bentonite slurry (BS). The BS has been used about seventy years to temporarily support the excavations. More recently, polymer support fluids (PSF) gained much popularity and are widely used compared to bentonite support fluids. The PSF are categorized into natural (pure) and synthetic polymers. Physico-chemical properties of PSF are different than BS irrespective of the quite similarity in the mode of action. Synthetic polymer fluids are molecularly engineered fluids that can be a popular alternative of conventional BS deployed as excavation support fluids in different foundation applications such as diaphragm wall panels and pile bores. The synthetically engineered fluids of polymers (water-soluble) are different from conventional BS. The PSF offer additional benefits because their use is cost effective, eco-friendly, and these polymers need smaller site footprint as well as easy preparation, mixing, handling, management and ultimately the final disposal. Nevertheless, synthetic polymers have advantage over bentonite, however, foundation engineers and scientists have also certain concerns about their use because of their performance related issues. For an efficient use of polymers, specific properties and in situ behavior of polymers as well as their sorption onto the soils must be recognized because the polymer concentration in the solution is decreased with time during their use. The present manuscript reviewed the relative performance of excavation support fluids and displayed an arranged marriage of physicochemical and rhelogical properties of natural and synthetic excavation support fluids used in the foundation industry. This information will be highly useful to scientific community for their future ventures and will lay a foundation to understand the mechanisms of stabilization in open and deep excavations.

On the Responses of Braced Diaphragm Wall Supporting Deep Excavation Subjected to Asymmetric Surcharge Loads

As cities grow, so does the need for housing and transportation infrastructure, necessitating deep excavations. Near the deep excavation, especially in the urban centers, there are existing structures whose loads are often different, resulting in asymmetric loading of the excavation system and different behavior on each side of the excavation. In this study the strut forces, lateral deformations, bending moments on each wall, as well as the settlements and heaves of the soil behind both walls in the asymmetrically loaded strut-supported excavation system are determined using the finite element method (FEM). The analyzes are performed using Plaxis 2D v20, a computer software based on the FEM. In addition, regression analyses are performed on the results, and correlations that predict the relevant results depending on the surcharge loads are presented.

Effect of climate change on the behaviour of thermo-active diaphragm walls

Energy geo-structures are becoming more common as a renewable energy solution which utilises shallow geothermal energy to provide heating and cooling to buildings and civil infrastructure projects. There has been an upward trend in the use of thermo-active geo-structures in the United Kingdom, from 150 in 2005 to over 5000 in 2012 [2]. Studies so far have shown that diaphragm walls subjected to combined thermo-mechanical loading show overall increases in lateral displacements, bending moments, shear forces, axial forces, and settlements on the retained side with thermal cycles [6, 7, 8].
 This study uses a variation of a validated numerical model [4] to predict the behaviour of thermo-active diaphragm walls in the longer-term including accounting for the influence of climate change. This numerical model also assesses the impact of different modelling assumptions on the model output by comparing a simplified model with a more complex model where atmospheric temperatures affecting ground surface temperatures are included. Research from the IPCC shows increases in ambient temperatures and in maximum extreme temperatures as a result of climate change. Two models are compared in the IPCC report [5], Representative Concentration Pathway (RCP) 2.6 where governments across the world work together to meet the recommendations in the report to reduce overall warming, and RCP8.5 where the current trends of heating continue without any governmental interventions. According to climate model RCP2.6, global mean surface air temperatures will increase by around 1.5°C and extreme daily temperatures (i.e. days where temperatures exceed expected temperatures for the time of year) will increase by around 2°C over the 50-year period chosen for this study, whilst using RCP8.5 global mean surface air temperature increases by approximately 3°C and extreme daily temperatures increase by approximately 5°C.
 This study uses the same model geometry as a model validated through centrifuge testing [4] which is a 5m deep cantilever diaphragm wall, like those that would be used in deep excavations for open-topped tunnels in large civil infrastructure projects. The numerical model was developed using the semi-coupled thermo-hydro-mechanical (THM) thermal module available with PLAXIS 2D and uses the HS-Small soil model [3] to allow for variation in shear modulus at small strains (i.e. those associated with retaining walls) to be captured more accurately. Thermal loads were applied by applying heat flows through a plate element with the same mechanical properties of the model diaphragm wall used in centrifuge testing. This model attempts to capture the influence of atmospheric temperatures by applying thermal boundary conditions to the ground surface as well as to the thermo-active diaphragm wall. Studies have demonstrated that a more complex model capturing atmospheric temperatures increases the impact of thermal loading [4], whilst also capturing a more realistic temperature profile throughout the entire depth of the soil body both adjacent to the wall and in the free field condition. In this study, atmospheric temperatures were captured in RCP2.6 by cycling between 30°C and -5°C over the course of the cycle to represent a typical ‘hottest’ and ‘coldest’ day of the year in cycle 1, increasing to 32°C and -5°C in line with the temperature increases described in the IPCC report [5]. Ambient mean temperatures between heating and cooling cycles increased from 20°C to 21.5°C over the 50-year period. In the same model, the temperature within the diaphragm
 wall cycled between 35°C and 10°C in cycle 1, representing the typical operation of a ground source heat pump (GSHP) in heating and cooling. These temperature inputs increased to 37°C and 10°C over the 50-year period. The RCP8.5 atmospheric temperatures cycled between 30°C and -5°C to represent summer and winter in cycle 1 and increase to 35°C and -5°C over the 50-year period. Thermal flows in the diaphragm wall cycled between 35°C and 10°C in cycle 1 and increased to 40°C and 10°C over the 50-year period. The results from this study show increases in lateral displacement, maximum bending moments, positive and negative shear forces and axial forces (compressive (-) and tensile (+)). These results are shown in Figure 1.
 Significantly, the RCP2.6 model shows that these increases begin to stabilise over the 50-year period, with the increases in the final cycles becoming negligible. With the RCP8.5 model these increases are increasing linearly at the end of the modelling period which can potentially have significant implications not only in terms of serviceability of the structure, but potentially on ultimate limit state as linear increases suggest that design limits will eventually be reached. The findings from this study generally agree with other similar studies, such as a study that analysed the geotechnical performance of energy piles with additional environmental loading as a result of climate change which found that additional compressive and tensile stresses are generated during heating and cooling phases, respectively [1].